Quote:
Originally Posted by Mikeg
Is that really how small the seeds are??
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Yes.
Quote:
Originally Posted by Mikeg
Really?? Whay are they so tiny?
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Don't really know why they opted to go the route of conservation of energy in creating a lot of smaller seeds w/o endosperm instead of fewer larger seeds w/ endosperm.
Maybe there was a period in time when the shift in evolution favored the plants to gradually become more and more mycoheterotrophic ("fungus eaters") rather than more dependent on photosynthesis. Perhaps for most orchids and plants, the shift to become more mycoheterotrophic stopped before the evolutionary process could be completed and things reverted back to an environment that favored photosynthesis.
From what I understand, and if I remember correctly, while fungus doesn't necessarily need light to survive (except for certain lichens), they can thrive off of radiation.
I'm kinda fuzzy on this. If anyone's able to get the details down on fungus and radiation that'd be cool.
There seems to be a number of physical evidence in orchids that suggests that this is exactly what happened.
The following is my hypothesis:
I believe that epiphytical orchids had developed roots that were capable of photosynthesis to capitalize and maximize growing and energy consumption in an environment that provided them with ample light energy for being under a tree canopy.
Then something happened and made the Earth have access to very limited amounts of solar energy, thus making the plants have to depend on their mycorrhizal symbionts more heavily for energy (which acted like a backup generator).
As time in a more dimly lit Earth progressed, something along the lines of the following examples of plants started to develop:
Limodorum spp.
Neottia spp.
Rhizanthella spp.
The above mentioned genera of terrestrial orchids are either leafless or have a very small number of leaves that have been reduced down to scales, which means they either cannot photosynthesize or have very limited photosynthetic capacity.
Other examples:
Chiloschista spp.
Dendrophylax spp.
Harrisella spp.
Polyrrhiza spp.
Taeniophyllum spp.
All "leafless" orchids. These are orchids that have poorly developed leaves that have limited photosynthetic abilities to some degree or another, or have leaves that have been reduced to microscopic scales, perhaps even in some, there aren't any at all. The only things left that did any photosynthesizing are the roots. I consider this an intermediary stage of going on the way to becoming fully mycoheterotrophic.
In the midst of all this, orchids may have also gradually evolved seeds that were more energy conservative and opted to forego endosperm and produce more seeds rather than fewer seeds.
I think that the gradual reduction in endosperm left for more energy to be put into creating a greater number of seeds for survival in a very harsh environment.
The presence of reduced endosperm reserves in certain species of orchid seeds, while most orchid species have opted to have seeds that are absent of endosperm, suggests to me that, at one point in time, orchids didn't rely as heavily on mycorrhizal fungi; but a shift in environmental factors pressured the orchid seeds to start to utilize what was there in greater abundance for energy at the time - mycorrhizal fungi.
Then the Earth reverted back to a brightly lit environment that favored photosynthesis, which is why I think there are still a lot of orchids that can still photosynthesize and the ones that were about to go leafless, remained in the intermediary stage. The ones that are either partially or fully mycoheterotrophic remained so, because there were enough micro-niches for them to survive.
There could be other reasons or details, but I think this is the major crux of what may have happened.
Contrary to common belief, orchid seeds are actually not that light in weight for their size. They tend more to drop like lead rather than drift around in the wind like dandelion seeds do.
Sewing orchid seed - 1
Linear Mode
